In the drilling, completion, and stimulation of hydrocarbon-producing wells, a variety of downhole tools are used. For example, it is often desirable to seal portions of a wellbore targeted for treatment. During fracturing operations, for instance, various fluids and slurries are pumped from the surface into a casing string and forced out into a surrounding subterranean formation, but only certain desired zones of interest should receive the fracturing fluid. It thus becomes necessary to seal the wellbore and thereby provide zonal isolation to target the treatment to the desired zone(s). Wellbore isolation devices, such as packers, bridge plugs, and fracturing plugs (i.e., “frac” plugs) are designed for these general purposes and are well known in the art of producing hydrocarbons, such as oil and gas. Such wellbore isolation devices may be used in direct contact with the formation face of the wellbore, with a casing string extended and secured within the wellbore, or with a screen or wire mesh.
After the desired downhole operation is complete, the seal formed by the wellbore isolation device must be broken and the downhole tool removed from the wellbore to allow hydrocarbon production operations to commence without being hindered by the presence of the downhole tool. Removing wellbore isolation devices, however, is traditionally accomplished by a complex retrieval operation that involves milling or drilling out a portion of the wellbore isolation device, and subsequently mechanically retrieving its remaining portions. To accomplish this, a mill or drill bit is attached to the distal end of a work string and conveyed into the wellbore until locating the wellbore isolation device, at which point the wellbore isolation device may be milled or drilled out. After drilling out the wellbore isolation device, the remaining portions of the wellbore isolation device may be grasped onto and retrieved back to the surface with the work string for disposal.
As can be appreciated, this retrieval operation can be a costly and time-consuming process. Consequently, wellbore isolation devices are increasingly being manufactured of degradable or dissolvable materials that dissolve under certain wellbore conditions or in the presence of certain wellbore fluids, and thereby preclude the need to drill or mill out the wellbore isolation device. Traditional wellbore isolation devices, however, can include up to thirty or more structural elements or components, each of which needs to be made of a degradable material and designed to degrade at a predetermined rate or within a predetermined time period. In practice, some component parts will dissolve quicker than others, which could lead to pre-mature release within the wellbore.